Muscadine grapes, from a grapevine (Vitis rotundifolia) native to the southeastern U.S., contain a somewhat different blend of beneficial micronutrients than other grape varieties. For example, muscadine grapes have higher concentrations of anthocyanins and ellagic acid. These differences appear to translate into more potent chemopreventive properties with respect to breast cancer. For instance, one study reported that muscadine grape polyphenols had greater inhibitory effect on triple negative (ER-/PR-/HER2-) breast cancer cell growth and survival than Cabernet Sauvignon (Vitis vinifera) polyphenols. Now a new study has reported that muscadine grape extract reduces proliferation in human epidermal growth factor receptor 2 positive (HER2+) breast cancer cells.

Best sources of muscadine polyphenols

Polyphenols are plant-based antioxidant micronutrients that may contribute to the color, smell or taste of foods. Grape skin and seed are more abundant sources of polyphenols than grape flesh. Nevertheless, the best sources are fresh red muscadine grapes (when available), muscadine grape juice, and to a lesser extent, muscadine grape jam. Like other red wines, muscadine wine is not recommended. The beneficial micronutrients in red wine do not mitigate the harmful effects of its alcohol content, according to available evidence.

Grape phytonutrients are not significantly present in grape seed oil (although cold-pressed virgin grape seed oil contains more of them than highly refined products). Grape seed oil does contain gamma-tocotrienol, a form of vitamin E with chemopreventive properties. However, grape seed oil primarily consists of the omega-6 fatty acid linoleic acid (approximately 70%, depending on grape variety), a level between than that found in safflower oil (79%) and soybean oil (51%). This makes grape seed oil a relatively abundant source of omega-6 fats, which should be noted by those who are attempting to reduce their ratio of omega-6 to omega-3 consumption.

We do not recommend taking grape seed extract for purposes of preventing or treating breast cancer because safe and effective levels of such supplementation have not been established. Grape seed extract requires more study to ensure that unintended adverse effects do not result from supplementation. One study found that the degree of mammary cancer chemoprevention by grape seed extract in rats depended on the diets fed to the rats. Another study found that grape seed extract has weak estrogenic activity.

Latest research finds muscadine extract inhibits HER2+ proliferation

The study referenced at the beginning of this news story was designed to investigate the impact of muscadine grape (Vitis rotundifolia) skin and seed extract (muscadine extract) on the proliferation of HER2+ breast cancer cells. Information concerning the therapeutic effects of extracts from muscadine grapes on cancer is limited. The muscadine grape, which is native to the warm, humid climate of the southeast U.S., contains high concentrations of anthocyanin 3,5-diglucosides, ellagic acid, ellagic acid precursors, and gallic acid, as well as flavan-3-ols and flavonols.

To conduct the study, the authors treated SKBR3 HER2+ breast cancer cells with increasing concentrations of a proprietary muscadine skin and seed extract from Piedmont Research & Development Corp. Concentrations from 10 to 40 μg/mL were found to significantly inhibit the proliferation of HER2+ cells in a dose dependent manner, with the greatest effect at 40 μg of phenolics/mL (58.4% inhibition). The authors also demonstrated that incubation of HER2+ cells with 30 μg/mL of muscadine extract reduced cell proliferation in a time-dependent manner (maximum of 49.2% reduction after 48 hours).

Additional analysis revealed changes in the AKT/mTOR pathway, which has been implicated in breast cancer. Muscadine extract-treated HER2+ cells had significantly reduced phospho-AKT and phospho-mTOR compared to untreated cells. The authors conclude that muscadine extract attenuates proliferation in HER2 positive breast cancer cells by reducing phospho-AKT, which in turn inhibits phosphorylation of mTOR. The results suggest that muscadine extract may serve as an effective treatment, alone or in combination with targeted drugs, for the treatment of HER2+ breast cancer, according to the authors.

Please see our article on HER2+ breast cancer diet for more information.